rustc_codegen_llvm: Restore the closure env alloca hack for LLVM 5.

src/librustc_codegen_llvm/mir/mod.rs

@@ -574,6 +574,25 @@ fn arg_local_refs(
  };
  let upvar_tys = upvar_substs.upvar_tys(def_id, tcx);
 
+ // Store the pointer to closure data in an alloca for debuginfo
+ // because that's what the llvm.dbg.declare intrinsic expects.
+
+ // FIXME(eddyb) this shouldn't be necessary but SROA seems to
+ // mishandle DW_OP_plus not preceded by DW_OP_deref, i.e. it
+ // doesn't actually strip the offset when splitting the closure
+ // environment into its components so it ends up out of bounds.
+ // (cuviper) It seems to be fine without the alloca on LLVM 6 and later.
+ let env_alloca = !env_ref && unsafe { llvm::LLVMRustVersionMajor() < 6 };
+ let env_ptr = if env_alloca {
+ let scratch = PlaceRef::alloca(bx,
+ bx.cx.layout_of(tcx.mk_mut_ptr(arg.layout.ty)),
+ "__debuginfo_env_ptr");
+ bx.store(place.llval, scratch.llval, scratch.align);
+ scratch.llval
+ } else {
+ place.llval
+ };
+
  for (i, (decl, ty)) in mir.upvar_decls.iter().zip(upvar_tys).enumerate() {
  let byte_offset_of_var_in_env = closure_layout.fields.offset(i).bytes();
 
@@ -585,7 +604,10 @@ fn arg_local_refs(
  };
 
  // The environment and the capture can each be indirect.
- let mut ops = if env_ref { &ops[..] } else { &ops[1..] };
+
+ // FIXME(eddyb) see above why we sometimes have to keep
+ // a pointer in an alloca for debuginfo atm.
+ let mut ops = if env_ref || env_alloca { &ops[..] } else { &ops[1..] };
 
  let ty = if let (true, &ty::TyRef(_, ty, _)) = (decl.by_ref, &ty.sty) {
  ty
@@ -595,7 +617,7 @@ fn arg_local_refs(
  };
 
  let variable_access = VariableAccess::IndirectVariable {
- alloca: place.llval,
+ alloca: env_ptr,
  address_operations: &ops
  };
  declare_local(